On a technical level, this could be shorter; you could leave out the part about escaping the castle grounds and skip straight to finding her father's allies. And please, you must must must guard against errors. In this context "parents" needs an apostrophe at the end: "parents' slaughter". "Fathers" should be "father's". "Saving her people" should be "save her people". Remember, the smaller the space the worse errors look, and you don't get much tighter than loglines.
Concept-wise, it's a very good thing you put the Tipping the Velvet comparison in there - otherwise this runs the risk of looking like a warmed-over Snow White and the Huntsman (sorry, it' the first thing springing to mind). I love the girl-girl angle (I assume that's what you meant with your comparisons?) and your logline absolutely needs to work that in. How can you make it clear there's a potential romance between Aewyn and the Amazon while retaining brevity and imparting the necessary information?
I'll throw a for-instance at you. You can keep it or you can send it on back: "Princess Aewyn escapes the slaughter of her parents and begins raising an army, among which is (Amazon hottie's name), a woman who stirs in Aewyn a passion for more than revenge."
Now, is that a bit bodice-ripper-ish? Unquestionably. But hopefully it can get you started toward something more refined. It's the kind of direction I think would best serve your concept, and it is a worthwhile concept.
A final note: "Aewyn" is a bit too similar to Tolkien's ?owyn of Rohan.
